GEOLOGICAL CONCEPTS

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GEOLOGICAL CONCEPTS

• FIVE STEPS TO BECOMING A
• GEOLOGICAL DETECTIVE!

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OUR GOAL TO INTERPRET GEOLOGICAL STRUCTURES WE
SEE, LIKE THE ROADCUT DEPICTED BELOW
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THE 5 CONCEPTS

• UNIFORMITARIANISM
• ORIGINAL HORIZONTALITY
• LATERAL CONTINUITY
• SUPERPOSITION
• LAW OF CROSS-CUTTING RELATIONSHIPS

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CONCEPTUNIFORMITARIANISM
USING HISTORY, WE STUDY THE PAST TO UNDERSTAND
THE PRESENT
BUT USING UNIFORMITARIANISM, WE STUDY THE PRESENT
GEOLOGICAL PROCESSES TO UNDERSTAND THE PAST
GEOLOGICAL PROCESSES (EVENTS THAT HAPPENED
MILLIONS OF YEARS AGO)

• DEFINITION GEOLOGICAL PROCESSES HAPPENING TODAY
  HAPPENED IN THE PAST

EXAMPLE TO UNDERSTAND MOUNTAINS THAT FORMED
MILLIONS OF YEARS AGO, WE STUDY HOW MOUNTAINS ARE
FORMING TODAY.
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WHAT ARE THE HORIZONTAL LINES?
APPLICATION 1 OF UNIFORMITARIANISM
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CLUE FROM PRESENT PROCESS
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HERE IT IS AGAIN
USING TIME LAPSE PHOTOGRAPHY
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ANCIENT LAKE
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DRYING UP
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LEAVING TERRACE LINES
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JUST LIKE THE RESERVOIR
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WHAT IS THIS?
APPLICATION 2 OF UNIFORMITARIANISM
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FROM ANCIENT MUD FLAT
CLUE FROM PRESENT PROCESS
OR SAND DUNE
THEY MUST HAVE SOLIDIFIED INTO ROCK
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EXPLAIN THIS SOLID ROCK
APPLICATION 3 OF UNIFORMITARIANISM
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GRAVEL
CLUE FROM PRESENT PROCESS
RIVERBED
BEACH
THEY MUST HAVE SOLIDIFIED INTO ROCK
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FROM UNIFORMITARIANISMCOMES THE OTHER 4 CONCEPTS

• ORIGINAL HORIZONTALITY
• LATERAL CONTINUITY
• SUPERPOSITION
• LAW OF CROSS-CUTTING RELATIONSHIPS

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CONCEPTORIGINAL HORIZONTALITY

• SEDIMENT LAYERS ARE USUALLY DEPOSITED
  HORIZONTALLY

THUS, LOOK FOR LAYERS NO LONGER HORIZONTAL, TO
RECOGNIZE THAT FORCES ACTED ON THE LAYERS AFTER
FORMATION
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APPLICATION OF ORIGINAL HORIZONTALITY
FINDING TILTED AND FOLDED LAYERS
WHAT HAPPENED TO THE LAYERS HERE?
THEY WERE FOLDED
BY FORCES PUSHING TOGETHER
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SUMMARY OF ORIGINAL HORIZONTALITY

• SEDIMENT LAYERS ARE USUALLY DEPOSITED
  HORIZONTALLY
• SO, LOOK FOR LAYERS THAT ARE NOT HORIZONTAL,
  MEANING SOME FORCE ACTED ON THEM TO FOLD OR TILT
  THEM
• USE THIS CONCEPT TO FIND FOLDS AND TILTED ROCK
  LAYERS

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CONCEPTLATERAL CONTINUITY

• ROCK LAYERS CAN BE TRACED ACROSS WIDE AREAS

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APPLICATION OF LATERAL CONTINUITY
WHAT HAPPENED TO THE LAYERS HERE?
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APPLICATION OF LATERAL CONTINUITYFINDING FAULTS
FORCES ACTED ON THE ROCK LAYERS TO BREAK THEM!
CREATING A FAULT (BROKEN ROCK LAYERS).
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2ND APPLICATION OF LATERAL CONTINUITY
WHAT HAPPENED TO THE LAYER BETWEEN THESE TWO
ARROWS?
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2ND APPLICATION OF LATERAL CONTINUITYFINDING
EROSION
EROSION REMOVED THE MATERIAL AS THE RIVER CUT
DOWNWARD
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2ND APPLICATION OF LATERAL CONTINUITYFINDING
EROSION
EROSION REMOVED PART OF THE LATERALLY CONTINUOUS
LAYERS AFTER THE LAYERS WERE FOLDED UPWARD
WHAT HAPPENED HERE?
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SUMMARY OF LATERAL CONTINUITY

• ROCK LAYERS ARE DEPOSITED (SO CAN BE TRACED)
  ACROSS WIDE AREAS
• SO, LOOK FOR BREAKS IN THE CONTINUITY
• AND USE THIS CONCEPT TO FIND FAULTS AND AREAS
  THAT HAVE EXPERIENCED EROSION

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CONCEPTSUPERPOSITION

• YOUNGER ROCK LAYERS
• USUALLY OVERLIE
• OLDER ROCK LAYERS

AS NEW SEDIMENT DEPOSITS ON TOP OF EXISTING
SEDIMENT
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WHICH ROCK LAYER IS YOUNGER?
APPLICATION OF SUPERPOSITION
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ROCK LAYER A IS YOUNGER
APPLICATION OF SUPERPOSITIONDETERMINING
RELATIVE AGES OF LAYERS
NOT B
A
ltltltltlt YOUNGER OLDER gtgtgtgtgt
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WHICH ROCK LAYER IS YOUNGER?
2ND APPLICATION OF SUPERPOSITION
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ROCK LAYER A IS YOUNGER
2ND APPLICATION OF SUPERPOSITIONDETERMINING
RELATIVE AGES OF LAYERS
OR B?
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SUMMARY OF SUPERPOSITION

• YOUNGER ROCK LAYERS USUALLY OVERLIE OLDER ROCK
  LAYERS
• SO, LOOK FOR ROCK LAYERS ONE ON TOP OF THE OTHER
• USE THIS CONCEPT TO FOLLOW THE HISTORICAL
  SEQUENCE OF EVENTS HAPPENING AT A GIVEN SPOT

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CONCEPTLAW OF CROSS-CUTTING RELATIONSHIPS
INTRUDING ROCK IS YOUNGER THAN THE ROCK INTO
WHICH IT INTRUDES
MAGMA INTRUSION CALLED A DIKE
MOLTEN ROCK CALLED MAGMA
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APPLICATION OF CROSS-CUTTING RELATIONSHIPS
WHICH ROCK IS YOUNGER?
A?
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APPLICATION OF CROSS-CUTTING RELATIONSHIPS DETERM
INING RELATIVE AGE OF ROCKS
B IS YOUNGER BECAUSE B INTRUDED THROUGH LAYER
A
INTRUSION
A?
OR B?
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SUMMARY OF CROSS-CUTTING RELATIONSHIPS

• INTRUDING ROCK IS YOUNGER THAN THE ROCK INTO
  WHICH IT INTRUDES
• SO LOOK FOR INTRUSIONS, ROCK THAT IS DIFFERENT
  FROM AND CUTS THROUGH OTHER TYPES OF ROCK
• USE THIS CONCEPT WITH SUPERPOSITION TO FOLLOW THE
  HISTORICAL SEQUENCE OF EVENTS HAPPENING AT A
  GIVEN SPOT

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REVIEW 1
1. HOW CAN YOU APPLY ORIGINAL HORIZONTALITY?
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A. LOOK FOR LAYERS NOT HORIZONTAL TO FIND FOLDS
AND TILTED ROCK
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2. HOW CAN YOU APPLY LATERAL CONTINUITY?
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A. LOOK FOR BREAK IN CONTINUITY TO FIND FAULTS
AND EROSION
3. HOW CAN YOU APPLY SUPERPOSITION?
A. TO DETERMINE THE HISTORICAL SEQUENCE OF
EVENTS HERE
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REVIEW 2

• WHICH IS YOUNGER

1. LAYER 1 OR 2?
A. LAYER 2SUPERPOSITION
2. LAYER 2 OR DIKE B?
A. DIKE BCROSS-CUTTING REL.
3. VOLCANO A OR B?
A. VOLCANO A
LAYER 2
4. FAULT A OR B?
LAYER 1
A. FAULT A